gatt_disconnect: Remove L2CA_CancelBleConnectReq

When the link is not up, we need to cancel create connection.  In this
case, calling L2CA_CancelBleConnectReq() is just removing the gatt
direct connect client CONN_MGR_ID_L2CAP.  Then we clean up tcb.

Test: cert/run
Tag: #gd-refactor
Bug: 141555841
Change-Id: Ie294b7ad9c4429af71c45afe7b0a1ae6327dee2c